3D miniature preconcentrator and inlet sample heater

ABSTRACT

The present invention relates to a three dimensional preconcentrator and inlet heater. The preconcentrator consists of a substrate with passageways, a conductive material coated to the top and the bottom of the substrate and an adsorbent coating covering the entire substrate. This substrate is suspended in a holding frame by a connecting bridge. The preconcentrator may also include a resistor and a proportional-integral-differential controller. The device may be used inline with a detector and can be retrofitted to existing devices. An array of preconcentrators may also be formed. The invention also relates to methods of use of the preconcentrator and methods of manufacture. A method of use includes contacting an analyte and a preconcentrator, allowing the analyte to adsorb to the preconcentrator and then desorbing the analyte. A method of manufacture involves applying the adsorbent coating by misted chemical deposition.

FIELD OF THE INVENTION

The present invention relates to a preconcentrator and inlet sampleheater for an analytical instrument. More particularly, the presentinvention relates to a micro-machined preconcentrator and inlet sampleheater with a three-dimensional structure, integral heating, and asemiconductor substrate.

BACKGROUND OF THE INVENTION

In analytical chemistry, preconcentrators have been used for many yearsto collect molecules that are present in low concentrations. Analyticalinstruments may not be able to detect molecules in such lowconcentrations. Preconcentrators accumulate and concentrate one or morechemical species of interest over time, so that the analyticalinstruments can detect the molecule. Thus, preconcentrators increase thesensitivity of analytical techniques such as, e.g., gas chromatography,mass spectrometry, and ion mobility spectrometry (IMS).

Preconcentrators are particularly useful to aid in the detection oftrace compounds such as drugs, explosives, and other toxic agents. Asthese compounds are typically found in the field, battery-poweredportable detectors have been developed.

The key feature of a preconcentrator is the ability to adsorb an analyteand then release it at a specific temperature. To adsorb the analyte,special materials called adsorbent resins have been developed. Adsorbentresins are typically high surface area powders and the nature of theanalyte determines the choice of resin.

Existing preconcentrators usually consist of an adsorbent ‘slug’ insidea tube. The sample passes through the tube and analytes adsorb onto theslug. When enough analyte has accumulated, the slug is heated to releasea concentrated ‘plume’ of analyte into the detector for techniques suchas e.g. IMS. These preconcentrators have a low surface area to volumeratio, requiring a long time to accumulate a sufficient quantity ofanalyte. Furthermore, due to a pressure drop across the preconcentrator,inline use with existing detectors may require changing the internal airhandling. Such changes can be difficult, expensive and even precluderetrofitting of preconcentrators to an existing device. The slug is alsolarge requiring a fair amount of time and energy to release the analyte.This energy consumption poses a particular problem when preconcentratorsare used in portable detection systems as it lowers the battery life.

For portable systems, micro-machined preconcentrators have beendesigned. Typical inline micro-machined preconcentrators consist of athin film serpentine structure with an adsorbent coating on top. Thestructure can have thickness in the order of microns and consequently isquite fragile. The heating element is external to the device, limitingthermal efficiency. A break in the structure, which also serves as theheating track, will ordinarily cause complete failure.

The surface area of such concentrators is essentially the surface areaof the top of the structure, as the thickness is negligible. As aresult, such devices have a relative low surface area to which theanalyte adsorbs. Furthermore, because of their low surface area it takesa longer time to preconcentrate the analyte. Once sufficient analyte hasaccumulated, current is passed through the structure and causesdesorption. Since the heating of the preconcentrator is often notuniform, additional time and energy are required to desorb the analyte.Furthermore, due to the non-uniform heating, it is difficult toaccurately control desorption of the analyte.

Micro-machined preconcentrators may be mounted inline to the detector orexternally. In an external preconcentrator, the preconcentrator locatedinside a chamber and the analyte enters through an inlet port and leavesthrough an outlet port. Such preconcentrators are disadvantageous inthat they add complexity to the apparatus and thus hinder furtherminiaturization.

U.S. Pat. No. 6,239,428 to Kant discloses systems and methods of ionmobility spectrometry. The system may contain a preconcentrator whosetemperature is modulated between two temperatures. The preconcentratorhas permeable organic membranes or thin metal foils. Consequently, thepreconcentrator has low surface area and is quite fragile.

U.S. Pat. No. 6,171,378 to Manginelli et al. is illustrative of amicro-machined external preconcentrator. The preconcentrator contains asubstrate with a suspended membrane, which serves to support tworesistive heating elements on top of which an adsorbent coating isdeposited. Again, this preconcentrator does not maximize the surfacearea.

During the manufacture of a micro-machined preconcentrator,preconcentration material is placed on the device. One way to depositthe preconcentration material is to use ink jet deposition. This processemploys about 70,000 individual drops and is slow and serial. Ink jetdeposition lacks resolution to create ultra-small geometries and whencomplex features have to be printed, it can be prohibitively expensive.

There remains a need for a preconcentrator that does not create a largepressure drop, requires little energy to heat, can be micro-machined andimproves the preconcentration abilities. There also remains a need for acheap, efficient, and accurate method of manufacture of a micro-machinedpreconcentrator.

SUMMARY

Accordingly, one aspect of the present invention is directed to apreconcentrator that substantially obviates one or more of the problemsdue to the limitations and disadvantages of the related art.

Additional features and advantages of the invention are set forth in thedescription, which follows, and will be apparent, in part, from thedescription, or may be learned by practice of the invention. Certainobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof, as well as the appended drawings.

A preconcentrator according to the instant disclosure illustrativelycomprises: a substrate with passageways therethrough; a conductivematerial, such as a metal, covering the top and bottom of the substrate;a top electrical lead connected to the material on the top of thesubstrate; a bottom electrical lead connected to the material on thebottom of the substrate; an adsorbent coating disposed on top and bottomof the material and along the inside of the passageways. Thepreconcentrator may also include a holding frame; and a connectingbridge connecting the substrate to the holding frame. Thethree-dimensional structure of the preconcentrator can advantageouslycreate a large surface area to which an analyte may adsorb. Furthermore,the preconcentrator can have an integral heating element and a lowthermal mass, making it ideal for battery operation.

The substrate, holding frame and connecting bridge can be silicon. Theadsorbent coating can be polydimethylsiloxane (PDMS). In one embodimentof the invention, the preconcentrator is placed inline with a detector.In another embodiment, the preconcentrator is used as an inlet heater.

The preconcentrator may optionally include a temperature-variableresistor for temperature sensing. When the preconcentrator has such aresistor, a proportional-integral-differential controller may be used tocontrol the preconcentrator temperature.

When used for retrofitting, the preconcentrator further includes asupport. This support may contain a structural polymer such as TEFLON®,ceramic or polyetheretherketone (PEEK).

One embodiment of the invention includes an array preconcentrator, whichcontains at least two coated substrates connected to each other by aconnecting bridge with all substrates sharing the same holding frame.Each coated substrate typically includes passageways therethrough, acoating (e.g. metal) on the top and bottom of the substrate, and anadsorbent coating covering the substrate and electrical leads. In thisarray, optionally each coated substrate may selectively adsorb adifferent analyte of interest. The substrate, holding frame andconnecting bridge may advantageously contain silicon.

Another embodiment of the invention is a method of preconcentrating ananalyte comprising the steps of contacting the analyte and apreconcentrator, adsorbing the analyte to the adsorbent coating of thepreconcentrator at a temperature and for a period of time sufficient toallow the analyte to adsorb, and releasing the analyte from theadsorbent coating. The preconcentrator may contain: a substrate withpassageways therethrough; a conductive material covering the top andbottom of the substrate; a top electrical lead connected to theconductive material covering the top of the substrate; a bottomelectrical lead connected to the conductive material covering the bottomof the substrate; and an adsorbent coating on top of the conductivematerial and along the inside of the passageways. The preconcentratormay also include a holding frame; and a connecting bridge connecting thesubstrate to the holding frame. The preconcentrator may be mountedinline with the detector. The substrate may include silicon. Optionally,the preconcentrator may further contain a temperature-variable resistoror a resistor and a proportional-integral-differential controller.

In one embodiment of the method of preconcentration, the step ofcontacting the analyte with the preconcentrator comprises passing theanalyte over the surface of the preconcentrator.

Another embodiment of the invention includes a method of manufacturingthe preconcentrator comprising the steps of: supplying a substrate;providing passageways through said substrate; coating the top and bottomof said substrate with a conductive material; coating the top of theconductive material and the inside of the passageways with an adsorbentcoating using misted chemical deposition. The method may further includethe step of attaching electrical leads to said conductive material.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a cross-sectional view of a preconcentrator according to anembodiment of the present invention.

FIG. 2 is an electron micrograph of a cross-section of a preconcentratoraccording to one embodiment of the present invention.

FIG. 3 is a perspective view of a preconcentrator according to oneembodiment of the invention.

FIG. 4 is a scanning electron micrograph of a preconcentrator accordingto one embodiment of the invention.

FIG. 5 is a cross-sectional view of the preconcentrator shown in FIG. 1and illustrates a method of using the preconcentrator according to oneembodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. FIG. 1 is a cross-sectional diagram of a preconcentrator 100according to an embodiment of the present invention. The preconcentrator100 includes a substrate 102, illustratively, a rectangularparallelipiped, with passageways 104 running between top and bottommajor surfaces, a conductive material 106 covering the top and bottommajor surface, except for the passageways, a top electrical lead 110, abottom electrical lead 112, and an adsorbent coating 114 on the outersurfaces of electrical leads 110, 112. Top electrical lead 110 isconnected to conductive material 106 on the top side of the substrate.Bottom electrical lead 112 is connected to conductive material 106 onthe bottom side of the substrate. Electrical leads 110, 112 provide forpassage of current through the conductive material and substrate so thatthe entire preconcentrator may be used as a heating element when avoltage is applied across conductive material 106.

Preconcentrator 100 is a three-dimensional preconcentration device withan integral heating element. The preconcentrator may be micro-machinedor manufactured using conventional machining and techniques.

The exposed surface area of preconcentrator 100, to which the analyte ofinterest adsorbs as a sample passes through the preconcentrator,consists of the area at the top and bottom of the substrate 102 as wellas on the inside surfaces of passageways 104. Passageways 104 help tomaximize this exposed surface area and create a three-dimensionaladsorption surface. Thus, preconcentrator 100 has an optimal exposedsurface area, a large surface to volume ratio, and an extremely fastpreconcentration time. In one preferred embodiment of the invention, thepreconcentrator has an increased exposed surface area more than abouttwenty fold when compared to thin-substrate preconcentrators. Inalternate embodiments of the invention, the preconcentrator has anincrease in exposed surface area from about two fold to about onehundred fold when compared to thin-substrate preconcentrators.

In another embodiment of the invention, preconcentrator 100 issubstantially planar. In an alternate embodiment, the preconcentratorhas further surface features that increase the total exposed surfacearea. Differential etching of the substrate may create such additionalsurface features.

The preconcentrator may be fabricated in various thicknesses. In oneembodiment of the invention, the preconcentrator has a thickness in therange from about 10 microns to about 1000 microns, alternatively fromabout 20 microns to about 150 microns, alternatively from about 125microns to about 350 microns, alternatively from about 200 microns toabout 600 microns, alternatively from about 450 microns to about 750microns, alternatively from about 650 microns to about 1000 microns. Inan alternate embodiment, the preconcentrator has a thickness from about1 mm to about 50 mm, alternatively from about 2 mm to about 11 mm,alternatively from about 9 mm to about 20 mm, alternatively from about15 mm to about 25 mm, alternatively from about 22 mm to about 30 mm,alternatively from about 28 mm to about 39 mm, alternatively from about37 mm to about 44 mm, alternatively from about 43 mm to about 50 mm. Inanother embodiment, the preconcentrator has a thickness from about 500microns to about 1500 microns, alternatively from about 550 microns toabout 670 microns, alternatively from about 630 microns to about 760microns, alternatively from about 740 microns to about 850 microns,alternatively from about 820 microns to about 930 microns, alternativelyfrom about 910 microns to about 1100 microns, alternatively from about990 microns to about 1120 microns, alternatively from about 1110 micronsto about 1240 microns, alternatively from about 1230 microns to about1390 microns, alternatively from about 1380 microns to about 1450microns, alternatively from about 1420 microns to about 1500 microns.

Advantageously, particularly for use in portable detectors, apreconcentrator according to the instant disclosure is extremely robust.The structure can be exposed to much higher air pressure, may sufferdamage, and remain operable. This robustness is due to substrate 102,which is many times as thick as membrane substrates and extremely rigidthereby creating a firm mounting surface for the preconcentrator.

Substrate 102 may include any material that is rigid, can bemicro-machined, and is strong enough to have a conductive materialdeposited on its surface. This choice of material allows the substrateto remain rigid despite having passageways. To facilitate heating andreduce power consumption, the substrate 102 ideally should not have alarge thermal mass. Examples of suitable substrate materials includesemiconductor substrates, such as e.g. gallium arsenide or silicon ordielectric materials such as glass, quartz, resins, and plastics. In oneembodiment, the substrate is a metal. In another embodiment, thesubstrate is an SOI wafer. In one embodiment, the substrate is nothighly insulating.

The passageways 104 in preconcentrator 100 may take many shapes otherthan the cylindrical holes shown in FIG. 1. Through use of semiconductormanufacturing techniques, such as deep reactive ion etching, the exactpatterning of the passageways 104 can be varied. In another embodiment,the passageways are square holes. In another embodiment, the passagewaysare slots. In alternate embodiments, the passageways may be serpentinechannels.

The large amount of open area in the preconcentrator 100 created by thepassageways 104 results in a low-pressure drop across the substrate.This low pressure drop makes the preconcentrator particularly suitablefor inline retrofitting to existing detectors for most analyticaltechniques such as chromatography, mass spectrometry, IMS and fieldasymmetric ion mobility spectrometry (FAIMS), without altering fluidicsor changing existing pumps. Thus, an existing device can bepreconcentrating, while operating in a normal detection mode, therebyimproving the device's sensitivity. The pressure drop and flow raterelated to an interdigitated geometry is given by the followingequation:

Q=(N×w×h ³ ×P)/(12×L×μ)

where: μ is dynamic viscosity (Air=1.808 10⁻⁵ N s/m² at 20° C.)

-   -   N is number of drift regions in parallel    -   L is length of drift region (m)    -   h is height (m)    -   w is width of drift region (m)    -   Q is gas flow (m³/s)    -   P is pressure (N/m²)

Based on the above equation, one of ordinary skill in the art candetermine the appropriate dimensions of a preconcentrator according tothe instant disclosure.

Conductive material 106 is a material (e.g. metal) that conductselectricity. Similarly, top electrical lead 110 and bottom electricallead 112 are made from a conductive material that conducts electricity.Any conductive material known in the art is suitable for the instantdisclosure. The conductive material may be, for example, gold, copper,platinum, molybdenum, titanium, chromium, tungsten, or combinationsthereof. In one embodiment, the conductive material is a coated Tibarrier layer such as a Ti barrier layer coated with Aluminum.

The electrical leads are connected to a power supply. Any power supplyknown in the art is suitable for the instant invention. In someapplications, the power supply is advantageously a battery as thepreconcentrator has low thermal mass. The optimal voltage to be suppliedby the power supply depends on the choice of substrate and desiredoperating parameters. In one embodiment, the power supply applies fromabout 0.1 volts to about 100 volts, alternatively from about 0.5 voltsto about 10 volts, alternatively from about 1 volt to about 15 volts,alternatively from about 10 volts to about 25 volts, alternatively fromabout 20 volts to about 50 volts, alternatively from about 35 volts toabout 80 volts, alternatively from about 55 volts to about 85 volts,alternatively from about 80 volts to about 100 volts the substrate. Inanother embodiment of the invention, the power supply is a battery.

In one embodiment particularly suitable for FAIMS, the power supplyapplies from about 0 volts to about 40 volts, alternatively from about0.1 volts to about 0.5 volts, alternatively from about 0.3 volts toabout 1 volt, alternatively from about 0.9 volts to about 10 volts,alternatively from about 9 volts to about 15 volts, alternatively fromabout 13 volts to about 25 volts, alternatively from about 23 volts toabout 35 volts, alternatively from about 30 to about 40 volts.

A voltage applied between the electrical leads causes a current to flow.This current, without being bound by theory, leads to a Joule effect,which heats the preconcentrator, thereby leading to desorption of theanalyte. The heating of the device is extremely uniform, as theconductive material creates an integral, continuous, distributed heatingelement. Furthermore, due to the low thermal mass of thepreconcentrator, a low energy input is necessary and heating occursquickly.

The adsorbent coating 114 covers conductive material 106 and theinterior surfaces of passageways 104. By covering the conductivematerial and interior surfaces, the adsorbent coating causes the heatingelement to be an internal heating element. This advantageously maximizesheating while minimizing power consumption. The ability of the adsorbentcoating to adsorb an analyte of interest depends on chemicalselectivity, steric selectivity or both. Adsorbent coatings are commonlyknown in the art and any such coating may be used

In one embodiment of the invention, the adsorbent coating ispolydimethylsiloxane (PDMS).

In some embodiments of invention, adsorbent coating 114 selectivelyadsorbs a plastic explosive or a chemical signature thereof. Thus, thecoating may be selective for e.g. nitroglycerine (NG), dinitrotoulene(DNT), trinitrotoluene (TNT), pentaerythritoltetranitrate (PETN),cyclotrimethylenetinitramine (RDX), trinitrophenyl-n-methylnitramine(Tetryl), or volatile taggant compounds such2,3-dimethyl-2,3-dinitrobutane (DMNB) or mononitrotoluene. In otherembodiments, the adsorbent is selective for a nerve agent such asdimethyl methyl phosphonate (DMMP).

In other embodiments of the invention, the adsorbent coating selectivelyadsorbs an illicit drug or a chemical signature thereof. For example,the coating may be selective for mono- and diterpenes released bymarijuana, heroin, cocaine, or methamphetamines.

Analytes desorb from the adsorbent coating at different temperatures,highly dependent on the adsorption layer. Thus, by cycling through aseries of desorption temperatures it is possible to desorb differentclasses of analyte over time. Such cycling improves the selectivity andreduces the effects of interferants. In one embodiment of the invention,the adsorbent coating is selective for two or more analytes of interest,which desorb at different temperatures.

In one embodiment, the substrate is coated with one adsorbent coating.In another embodiment, the preconcentrator is coated with more than oneadsorbent coating. When the preconcentrator is coated with more than oneadsorbent coating, the coatings are applied in such a way that eachcoating occupies a unique area of the preconcentrator.

In another embodiment of the invention particularly suitable for heatingthe inlet stream that passes to the detector, the preconcentrator lacksan adsorbent coating.

In an alternate embodiment of the invention, the adsorbent coating has athickness from about 0.001 microns to about 1 micron, alternatively fromabout 0.01 microns to about 0.1 microns, alternatively from about 0.05microns to about 0.3 microns, alternatively from about 0.2 microns toabout 0.6 microns, alternatively from about 0.5 microns to about 1micron. In another embodiment of the invention, the adsorbent coatinghas a thickness of about 1 micron to about 10 microns, alternativelyfrom about 2 microns to about 7 microns, alternatively from about 5microns to about 10 microns.

FIG. 2 is a cross-sectional electron micrograph of the preconcentratoraccording to one embodiment of the invention. As shown in FIG. 2,preconcentrator 200 is a layered substrate 202 with passageways 204. Thelayered substrate 202 includes a substrate with a conductive materialcoating on the top and bottom and an adsorbent coating on the entiresurface. In this embodiment of the invention, the passageways 204 areslots. FIG. 2 illustrates how the slotted passageways in the substrateof the present invention create a large surface area to which an analytecan adsorb.

FIG. 3 is a perspective view of a preconcentrator according to oneembodiment of the invention. A connecting bridge 118 connect the coatedsubstrate 120 to a holding frame 122. The coated substrate 120 includespassageways therethrough, a conductive material coating on the top andbottom of the substrate, electrical leads, and an adsorbent coatingcovering the top of the conductive material and the inside surface ofthe passageways.

The connecting bridge 118 suspends coated substrate 120 in the holdingframe 122. The connecting bridge 118 is thin so as to reduce heat lossto the holding frame, thereby maximizing the effect of heating thesubstrate and lowering power consumption. In one embodiment, at leasttwo connecting bridges suspend coated substrate 120. In anotherembodiment, only one connecting bridge suspends the coated substrate. Inan alternate embodiment, at least four connecting bridges suspend thecoated substrate in the holding frame.

Holding frame 122 separates the analyte adsorbing area of thepreconcentrator from the rest of the device. Thus, holding frame 122 andconnecting bridge 118 thermally isolate the coated substrate 120 fromthe surrounding device. This allows the heating to be maximized andreduce power consumption.

The holding frame 122 and connecting bridge 118 may be made from anymaterial that is rigid and can be micro-machined. Advantageously,holding frame 122 and connecting bridge 118 have a low thermal mass tofurther increase the device's efficiency. Examples of such materialsinclude semiconductor substrates, such as e.g. gallium arsenide orsilicon or dielectric materials such as e.g. glass, quartz, resins, orplastics.

In an alternate embodiment of the invention, two or more coatedsubstrates are suspended within one holding frame. Each coated substratecontains a substrate, passageways therethrough, conductive materialcovering the top and bottom, adsorbent coating, and electrical leads asdisclosed herein. By using several coated substrates, it is possible touse different adsorbent coatings with preferential selectivity fordifferent analytes. Such coated substrates are connected to each otherand the holding frame by connecting bridges. Each coated substrate canbe individually addressed electrically to cause heating. The thinconnecting bridges provide thermal insulation thereby allowingindependent operation. When a holding frame is arranged in such a way, adetection array is created. In one embodiment of the invention, thecoated substrate contains a semiconductor substrate. In anotherembodiment, the coated substrate contains silicon. In an alternateembodiment, each coated substrate in the array has an adsorbent coatingselective for a plastic explosive.

FIG. 4 is a scanning electron micrograph of one embodiment of thepreconcentrator according to the invention. Clearly visible is thedeeply etched structure of preconcentrator 300 and four thin siliconconnecting bridges 302. Also visible is silicon substrate 304. Thedevice of FIG. 4 is incomplete. Prior to use, the remaining siliconsubstrate 304 would be machined away such that a gas stream could passthrough the device.

For temperature sensing, a temperature variable thin-film resistor maybe patterned onto the coated substrate. The resistance of this thin filmstructure changes with temperature. The temperature of thepreconcentrator can be determined by measuring the resistance, therebyproviding a measurement for closed loop control of the heatedpreconcentrator. In one embodiment of the invention, the preconcentratorfurther contains a single thin-film resistor. In another embodiment, thepreconcentrator contains a plurality (i.e., more than one) of thin-filmresistors. The advantage of using a plurality of resistors is to ensuretemperature uniformity and build in redundancy.

Alternatively, the preconcentrator may lack a thin-film resistor.

Use of a thin-film resistor enables closed loop operation. Thus, aproportional-integral-differential (PID) controller can be used toaccurately control the preconcentrator temperature. The circuit formedby a thin-film resistor and controller can be directly mounted on theceramic mount upon which the silicon die is fixed. In an alternateembodiment, the preconcentrator contains a plurality of thin-filmresistors and a proportional-integral-differential (PID) controller.

As previously discussed, the passageways in the preconcentrator mayadvantageously create a low-pressure drop across the preconcentrator,which makes it particularly suitable to retrofit to existing detectionsystems. For retrofitting, it may be desirable to mount apreconcentrator on a support, which is cheaper to produce than thepreconcentrator substrate, such that the preconcentrator is properlyplaced inline with the existing detector. A plurality ofpreconcentrators may be mounted on a support and attached inline of anexisting detector. The support may contain structural polymers such asTEFLON®, ceramic or polyetheretherketone (PEEK). In one embodiment, thesupport may be of a standard size with an adapter created for anexisting device. Thus, the same design of preconcentrator can be usedwith many different detectors, only requiring a change in the attachmentadapter.

FIG. 5 illustrates the method of using the preconcentrator of FIG. 1. Asdescribed with reference to FIG. 1, the preconcentrator 100 encompassessubstrate 102 with passageways 104 therethrough, conductive material106, top electrical lead 110, bottom electrical lead 112, and adsorbentcoating 114. Arrow 116 indicates the flow of the analyte through thethree-dimensional structure from the top to the bottom. After theanalyte is flowed through the preconcentrator and adsorbed for apredetermined preconcentration time, the structure is heated to releasean analyte plume 118 into a detector. The method of using thepreconcentrator comprises the steps of (a) contacting the analyte withthe adsorbent coating; (b) allowing the analyte to adsorb onto theadsorbent coating; and (c) heating the preconcentrator after adetermined period of time to release the concentrated plume of analyteinto the detector. In one embodiment, the step of contacting is achievedby flowing gas through the top of the preconcentrator with the flowexiting through the bottom. The step of heating the preconcentrator isachieved by applying a voltage across the electrical leads and allowing,without being bound by theory, the Joule effect to heat the device.

In an alternate embodiment, the method further includes monitoring thetemperature of the preconcentrator to ensure that the analyte ofinterest is released. In that embodiment, the preconcentrator containsat least one thin-film resistor and a proportional-integral-differential(PID) controller.

In another embodiment, the preconcentrator contains an adsorbent coatingthat adsorbs two or more analytes of interest, which desorb at differenttemperatures. In that embodiment, the step of heating thepreconcentrator further includes cycling the preconcentrator at thetemperatures at which the analytes of interest desorb.

As is well known in the art, only certain classes of analytes adsorbonto the adsorbent coating. This property combined with changing theinitial air flow can be used to improve the selectivity and reduce theoccurrence of false positives. In one embodiment of the invention, apreconcentrator is mounted inline of a detector, with an initial samplestream passing parallel to and over the preconcentrator, but not throughit. As the analyte of interest adsorbs to the preconcentrator,interferants are not adsorbed and continue on their path out of thedevice without ever contacting the inline detector. After a definedpreconcentration period, a stream of air is directed to pass through thepreconcentrator and the analyte of interest is desorbed from theconcentrator stream into the stream that leads to the inline detector.This particular embodiment is especially useful in military warfareagent detectors, when the adsorbent coating selectively adsorbs nerveagents. In a warfare environment, diesel, gasoline and jet fuels allcause significant false alarms when testing for nerve agents.

The preconcentrator according to the instant disclosure can be used formany detectors. The preconcentrator is useful for any detectiontechnique that can benefit from use of a preconcentrator. In oneembodiment, the preconcentrator is used inline for IMS. In anotherembodiment, the preconcentrator is used inline for FAIMS. In anotherembodiment, the preconcentrator is used inline for gas chromatography.In another embodiment, the preconcentrator is used inline for massspectrometry.

Standard IMS typically involves heating of the analyte to make thesystem more robust against environmental variation. Heating is alsodesirable to prevent analytes from sticking to the apparatus before theyreach the detector. The intrinsic heating ability of a preconcentratoraccording to the instant structure can be used to heat the analyte forIMS. Such inline heating is much more efficient as more of the analyteis heated. The surface area in contact with the flow is much greaterallowing for greater heat transfer. In one embodiment of the invention,a preconcentrator according the instant invention is used as an inlineheater for standard IMS. In another embodiment, a preconcentratorlacking an adsorbent coating is used as an inline heater for standardIMS.

The three-dimensional structure of a preconcentrator according to theinstant disclosure complicates preconcentrator manufacture. Thethree-dimensional features need to be coated with the adsorbent coating.In some embodiments, the layer is uniform. Thus, special manufacturetechniques are required. One technique suitable for applying is liquidsource misted chemical deposition. Misted chemical deposition converts aliquid source material into a very fine mist. Nitrogen then carries thismist to a deposition chamber. In the deposition chamber, sub-microndroplets coalesce on the wafer thereby covering it with a uniform liquidfilm. This film is then thermally cured leaving a thin surface layer ofsolid. Thus, this technique allows for a uniform coating of athree-dimensional structure. One embodiment of the invention is a methodof manufacturing of a preconcentrator comprising the steps of: a.supplying a substrate; b. providing passageways through said substrate;c. coating the top and bottom of said substrate with a conductivematerial; d. coating the entire substrate with adsorbent coating usingmisted chemical deposition. The method may further include the step ofattaching electrical leads to the conductive material.

In one embodiment of the invention, the mist deposited has a dropletsize from about 0.1 microns to about 0.3 microns, alternatively fromabout 0.15 microns to about 0.27 microns. In another embodiment, themethod further includes the step of mounting the substrate in a holdingframe.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

1. A preconcentrator comprising: a substrate with passageways therethrough; a conductive material covering the top and bottom of the substrate; a top electrical lead connected to the conductive material covering the top of the substrate; a bottom electrical lead connected to the conductive material covering the bottom of the substrate; a first adsorbent coating on a first portion of the conductive material and the inside of the passageways. a second absorbent coating on a second portion of the conductive material and the inside of the passageways.
 2. The preconcentrator of claim 1, wherein the substrate comprises silicon.
 3. The preconcentrator of claim 1, wherein the conductive material comprises a Ti barrier layer coated with Aluminium.
 4. The preconcentrator of claim 1, wherein one of the adsorbent coatings comprises polydimethylsiloxane.
 5. The preconcentrator of claim 1 further comprising; a holding frame; and a connecting bridge connecting the substrate to the holding frame.
 6. The preconcentrator of claim 5, wherein the holding frame and the connecting bridge comprises silicon.
 7. The preconcentrator of claim 1, wherein the preconcentrator is placed inline with a detector.
 8. The preconcentrator of claim 1, further comprising a temperature variable thin-film resistor.
 9. The preconcentrator of claim 8, further comprising a temperature-controlling proportional-integral-differential controller.
 10. The preconcentrator of claim 1, further comprising a support.
 11. The preconcentrator of claim 10 wherein the support is selected from the group consisting of TEFLON®, ceramic or polyetheretherketone.
 12. An array preconcentrator comprising: two or more preconcentrators, each preconcentrator comprising: a substrate with passageways therethrough, a conductive material covering the top and bottom of the substrate, a top electrical lead connected to the conductive material covering the top of the substrate, a bottom electrical lead connected to the conductive material covering the bottom of the substrate, and an adsorbent coating on top of the conductive material and along the inside of the passageways wherein at least one preconcentrator is individually addressed electrically.
 13. The array preconcentrator of claim 12, wherein each preconcentrator selectively adsorbs a different analyte of interest.
 14. The array preconcentrator of claim 12 further comprising a holding frame; and a connecting bridge connecting each preconcentrator to the other and to the holding frame.
 15. The array preconcentrator of claim 12, wherein the substrate, holding frame and connecting bridge comprise silicon. 16-22. (canceled)
 23. A method of manufacturing of a preconcentrator comprising the steps of: i) supplying a substrate; ii) providing passageways through said substrate; iii) coating the top and bottom of said substrate with a conductive material; iv) coating a first portion of the conductive material and the inside of the passageways with a first adsorbent coating; and v) coating a second portion of the conductive material and the inside of the passageways with a second absorbent coating.
 24. The method of claim 23 further comprising attaching electrical leads to said conductive material. 25-26. (canceled) 